Phenyldimethylsilyl ethers

H-abstraction is generally a facile process, which often competes with desired transformations. However, in this case it can be utilized favorably to translocate the radical to the desired position for further reaction. The radical precursor in 186 is just a modified phenyldimethylsilyl ether and is much more readily incorporated than the alternative product, which would possess the radical precursor at the site of cyclization. Exposure of (o-bromophenyl)dimethylsilyl ether 186 to Corey s catalytic tin hydride conditions [73] formed cyclopentane 187 as a 1 1.1 mixture of cisltrans isomers, in addition to some directly reduced product 188 (Scheme 10-60). 

Organolithiums. Allylic and benzylic alcohols undergo deoxygenative lithiation by treatment of their lithium alkoxides or phenyldimethylsilyl ethers with LDTBB. Alkyl phenyl selenides are also cleaved to give organolithium species that can react with aldehydes and allyl bromide. Some special alkyllithiums have been prepared from (2-pyridylthio)alkanes, which are available from carboxylic acids. ... 

Lewis acids, 15,72,106,108-11,112,116,128 Lithiation, 84 reductive, 68 o-Lithiation, 40 a-Lithiosilanes, 65, 68 o-Lithiosilyl enol ethers, 77 a-Lithiovinylsilanes, 69 Lithium bis(phenyldimethylsilyl)cuprate, 8,53... 

Secondly it has been found that a number of trialkylsilyl groups can be added stereoselectively to the /j-position of the C —C double bond in dioxanone 10 (derived from enantiomerically pure 3-hydroxybutanoic acid)23. In this case the presumed silylcuprate is generated from a chlorosilane and a higher-order organocuprate. In the example shown, with addition of phenyldimethylsilyl chloride, a diastereomeric ratio of 91 9 was obtained. Improved ratios were obtained with other groups (e g., 98 2 for trimethylsily 1), but unfortunately none of the latter were susceptible to oxidative cleavage. The first two steps of the procedure produce a mixture of 11 and its silyl enol ether, which is then desilylated to 11 by treatment with tetrabutylammonium fluoride. 

E)-l-Phenyl-2-buten-l-one added to a little dichloro[( + )-2,2 -bis(diphenylphos-phino)-l,r-binaphthyl]palladium(II) and 2 eqs. 1,1-dichloro-l-phenyl-2,2,2-tri-methyldisilane in benzene at room temp, under N2, the mixture refluxed for 2 h, cooled to —70°, treated with 1.9 M methyllithium in ether, stirred for 10 min then quenched with dil. HCl (S)-l-phenyl-3-(phenyldimethylsilyl)butan-l-one. Y 72% (87% e.e.). F.e. and conversion to p-hydroxyketones, also z //-a-alkyl-j3-hydroxy-derivs. by asym. 1,4-disilylation-alkylation, s. T. Hayashi et al., J. Am. Chem. Soc. 110, 5579-81 (1988) without asym. induction using Pd(PPh3)4 s. Tetrahedron Letters 29, 4147-50 (1988). 

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